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DS - GMAT Prep - Practice Test - Arithmetic Operations

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Misha
 Post subject: DS - GMAT Prep - Practice Test - Arithmetic Operations
 Post Posted: Thu Dec 25, 2008 10:11 pm 
If the operation (triangle symbol - using ^ for this example) is one of the four arithmetic operations addition, subtraction, multiplication, and division, is (6^2)^4 = 6^(2^4)?

(1) 3^2>3
(2) 3^1=3

The answer is A, but I can't figure out why. I can figure out why B is SUFF, but maybe my reasoning is wrong since I can't figure out A.[/list]
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Khalid
 Post subject: Re: DS - GMAT Prep - Practice Test - Arithmetic Operations
 Post Posted: Fri Dec 26, 2008 2:12 am 
Misha wrote:
If the operation (triangle symbol - using ^ for this example) is one of the four arithmetic operations addition, subtraction, multiplication, and division, is (6^2)^4 = 6^(2^4)?

(1) 3^2>3
(2) 3^1=3

The answer is A, but I can't figure out why. I can figure out why B is SUFF, but maybe my reasoning is wrong since I can't figure out A.[/list]


With statement 1:

this function can only be addition or multiplication

with either of these two operations the left side does indeed equal the right...sufficient

With statement 2

this function can be either multiplication or division

with multiplication the left and right side equal one another

with division it doesn't...

hence 2 is insuffcient.
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Misha
 Post subject: Re: DS - GMAT Prep - Practice Test - Arithmetic Operations
 Post Posted: Fri Dec 26, 2008 8:56 pm 
Ahh, I get it. I was thinking that the operation could only be one of the 4 arithmetic operations, rather than any combo of them if the math works out. I was taking a different meaning from the question. Thanks!
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RonPurewal
 Post subject: Re: DS - GMAT Prep - Practice Test - Arithmetic Operations
 Post Posted: Sun Dec 28, 2008 7:59 am 
Offline
ManhattanGMAT Staff


Posts: 7146
Khalid wrote:
Misha wrote:
If the operation (triangle symbol - using ^ for this example) is one of the four arithmetic operations addition, subtraction, multiplication, and division, is (6^2)^4 = 6^(2^4)?

(1) 3^2>3
(2) 3^1=3

The answer is A, but I can't figure out why. I can figure out why B is SUFF, but maybe my reasoning is wrong since I can't figure out A.[/list]


With statement 1:

this function can only be addition or multiplication

with either of these two operations the left side does indeed equal the right...sufficient

With statement 2

this function can be either multiplication or division

with multiplication the left and right side equal one another

with division it doesn't...

hence 2 is insuffcient.


extremely well done.

note the general takeaway here:
if you have a problem like this, in which a mystery symbol stands for one or more of a collection of operations, then your #1 goal is to figure out ANY AND ALL operations for which that symbol can stand.
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